title: Complexes with redox-active ligands: synthesis, structure, and electrochemical and photophysical behavior of the Ru(II) complex with TTF-annulated phenanthroline.
abstract: Ru(II) complexes with chelating ligands, 4',5'-ethylenedithiotetrathiafulvenyl[4,5-f][1,10]phenanthroline (L1), 1,3-dithiole-2-thiono[4,5-f][1,10]phenanthroline (L2), and 1,3-dithiole-2-ono[4,5-f][1,10]phenanthroline (L3), have been prepared and their structural, electrochemical, and photophysical properties investigated. Density functional theory (DFT) calculations indicate that the highest occupied molecular orbital of [Ru(bpy)2(L1)](PF6)2 (1) is located on the tetrathiafulvalene (TTF) subunit and appears ~0.6 eV above the three Ru-centered d orbitals. In agreement with this finding, 1 exhibits three reversible oxidations: the two at lower potentials take place on the TTF subunit, and the one at higher potential is due to the Ru(3+)/Ru(2+) redox couple. Complexes [Ru(bpy)2(L2)](PF6)2 (2) and [Ru(bpy)2(L3)](PF6)2 (3) exhibit only the Ru(3+)/Ru(2+)-related oxidation. The optical absorption spectra of all complexes reveal a characteristic metal-to-ligand charge transfer (MLCT) band centered around 450 nm. In addition, in the spectrum of 1 the MLCT band is augmented by a low-energy tail that extends beyond 500 nm and is attributed to the intraligand charge transfer (ILCT) transition of L1, according to time-dependent DFT calculations. The substantial decrease in the luminescence quantum yield of 1 compared to those of 2 and 3 is attributed to the reductive quenching of the emissive state via electron transfer from the TTF subunit to the Ru(3+) center, thus allowing nonradiative relaxation to the ground state through the lower-lying ILCT state. In the presence of O2, complex 1 undergoes a photoinduced oxidative cleavage of the central C═C bond of the TTF fragment, resulting in complete transformation to 3. This photodegradation process was studied with (13)C NMR and optical absorption spectroscopy.
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, Florida 32306, USA.
authors.forename: Lawrence K
authors.initials: LK
authors.lastname: Keniley
authors.forename: Nathalie
authors.initials: N
authors.lastname: Dupont
authors.forename: Lipika
authors.initials: L
authors.lastname: Ray
authors.forename: Jie
authors.initials: J
authors.lastname: Ding
authors.forename: Kirill
authors.initials: K
authors.lastname: Kovnir
authors.forename: Jordan M
authors.initials: JM
authors.lastname: Hoyt
authors.forename: Andreas
authors.initials: A
authors.lastname: Hauser
authors.forename: Michael
authors.initials: M
authors.lastname: Shatruk